Mass spectrometry (MS) has become a method of choice for fast and efficient identification of many types of larger molecules and molecular constructs including proteins, oligonucleotides, carbohydrates, monodispersed polyethylene glycols, etc. In general, a mass spectrometer comprises an ion source for generating ions from molecules to be analyzed, and ion optics for guiding the ions to a mass analyzer. A tandem mass spectrometer further comprises the ability to perform a second or further stages of mass analysis. This is typically referred to as MSn where the “n” superscript denotes the number of generations of ions. Optional separation or partial separation of analyte components prior to MS analysis may be achieved by liquid chromatography (LC), high performance liquid chromatography (HPLC) or ultra performance liquid chromatography (UPLC).
It is well-known in the art that biological polymers (i.e., intact proteins, oligonucleotides, etc.) subjected to electrospray ionization mass spectrometry give rise to broad distributions of ion charge states. Each of these charge states physically represents a fraction of the total distribution of ion signals correlating to that particular biological polymer species. By operating the mass spectrometer in full MS1 mode, a distribution of ions (mass-to-charge ratio, m/z) for a biological polymer species (mass) can be observed.
The charge state of a particular constituent ion may be unambiguously calculated by using m/z values of sequential charge state ions as in Equation 1, where H represents a proton (for positive ion mass spectrometry):z2=(m1/z1−H)/(m2/z2−m1/z1)  Equation 1:Where z1 and z2 are consecutive charges states (z1 is a higher charge state than z2); m1/z1 and m2/z2 are their respective m/z values and H is approximately 1.0 (Fenn, U.S. Pat. No. 5,130,538A).
A species' mass (M) can then be determined by using the calculated charge state value of that ion and the observed m/z value (Equation 2):M=z(m/z−H)  Equation 2:A charge state deconvolution algorithm may be utilized to simultaneously determine the entire spectrum of parent masses and constituent ion charge states for complex mass spectra involving multiple charge state distributions deriving from multiple parent species.
Due to well-known isotope effects, in general, the higher the molecular weight of an analyte in mass spectrometry, the broader the isotopic cluster will be in each charge state, and the more charge states the species will display. This results in a significant “dilution” of the analyte signal over these multiple charges states. Conventional serial isolation events especially in tandem mass spectrometry represent a bottleneck in the process of generating high quality tandem mass spectra. Methods of co-isolation or “multi-notch” isolation in mass spectrometry has been described previously (for example, see Senko, U.S. Pat. No. 9,048,074 B2 and cited references therein, incorporated herein in its entirety). Against the above background there remains a need for improving signal capture (relative abundance) of precursor and product ions in mass spectral analysis mass methods that involve larger analytes that show multiple charge states.